Water Research 36 (2002) 3867–3873 Removal of selenocyanate from water using elemental iron Xiaoguang Meng*, Sunbaek Bang, George P. Korfiatis Center for Environmental Engineering, Stevens Institute of Technology, Hoboken, NJ 08904, USA Received 1 August 2001; received in revised form 1 January 2002 Abstract Batch experiments were conducted to investigate the removal of selenocyanate (SeCN  ) from oil refinery wastewater and artificial wastewater with elemental iron [Fe(0)]. The chemical forms of selenium in the reacted solids were determined with X-ray photoelectron spectroscopy (XPS) and a sulfite extraction procedure. SeCN  was effectively removed from the wastewater with Fe(0) filings when the water pH was controlled at approximately 6. SeCN  was removed by Fe(0) through the formation of elemental selenium [Se(0)] and ferrous selenide. The possible chemical reactions between SeCN  and Fe(0) included deselenation of SeCN  and electrochemical reduction of Se(0) to selenide. A cost-effective process may be developed for the treatment of SeCN  in wastewater using Fe(0). r 2002 Elsevier Science Ltd. All rights reserved. Keywords: Selenocyanate; Selenium; Iron; Refinery; Wastewater; Deselenation 1. Introduction Selenium usually exists in four oxidation states in the environment, namely: selenate [Se(VI)], selenite [(Se(IV)], elemental selenium [Se(0)], and selenide [Se(II)]. Some oil refinery and mining wastewater contains significant concentrations of selenocyanate (SeCN  ) [1,2]. Sour crude oils produced from geological formations containing seleniferous marine shales often contain high levels of selenium. SeCN  and other reduced chemical species such as hydrogen sulfide are formed in the reducing environment. As crude oil is processed in refinery operations, selenium is concen- trated into the wastewater. The treatment of selenium in waters is a difficult challenge because the mobility of the selenium species is quite different. Conventional waste- water treatment processes such as coagulation with ferric salts are not effective for the removal of SeCN  because of its low affinity for iron hydroxide in a neutral pH range [2]. Aeration of the refinery wastewater shows no obvious oxidation of SeCN  at neutral pH. SeCN  can be oxidized to Se(IV) and Se(VI) in aerobic biological water treatment processes, analogous to thiocyanate oxidation. However, the biological pro- cesses are not effective for the removal of the selenium species. A two-step treatment has been investigated for the removal of SeCN  from oil refinery wastewater [2]. In the first step, SeCN  is converted to Se(IV) by oxidation with reagents such as ozone, hydrogen peroxide, and chlorine dioxide. Near complete oxidation of SeCN  by excess amounts of hydrogen peroxide at pH 11 can be achieved in approximately 2 h. Subsequently, Se(IV) is removed by coprecipitation with a ferric coagulant. Since the coprecipitation process is not effective for removing Se(VI), the oxidation step should be controlled carefully to minimize the formation of Se(VI). Manceau and Gallup [3] have reported that SeCN  can be removed with copper(II) by precipitation of an a- Cu(S 0.91 Se0 0.09 )CN solid solution. A high dose of cupric chloride dihydrate (2 g/L) must be added to the refinery wastewater to reduce the SeCN  concentration from 7 to o0.1 mg/L. Fe(0) is an effective and inexpensive material for the treatment of halogenated organic compounds [4,5] and for the removal of heavy metals from water [6–11]. Fe(0) *Corresponding author. Tel.: +1-201-216-8014; fax: +1- 201-216-8303. E-mail address: xmeng@stevens-tech.edu (X. Meng). 0043-1354/02/$ - see front matter r 2002 Elsevier Science Ltd. All rights reserved. PII:S0043-1354(02)00086-6